Production of polyurethane film/split leather laminate

ABSTRACT

PRODUCTION OF LAMINATED ARTICLES BY CASTING AND DRYING A LAYER OF A FULLY-REACHED POLYURETHANE MATERIAL ON A RELEASE TREATED CARRIER IN A MANNER TO FORM A MOISTUREVAPOR-PERMEABLE AND MOISTURE-IMPERMEABLE FILM, ONE OR MORE HIDES OF SPILT LEATHER BEING BONDED TO THE SUPPORTED FILM THROUGH A MOISTURE VAPOR-PERMEABLE TIE-COAT OF A COMPATIBLE ADHESIVE, AND THE CARRIER THEN BEING REMOVED. THE RESULTANT SPILT LEATHER POLYURETHANE FILM PRODUCT HAS THE APPERANCE AND OTHER PROPERTIES OF TOP-GRAIN LEATHER.

Aug. 6, 1974 R. G. SUTTON PRODUCTION OF POLYURETHANE FILM/SPLIT LEATHER LAMINATE Original Filed March 9, 1970 "United States Patent Oflice 3,827,930 Patented Aug. 6, 1974 V g 3827,9310 PRODU; N 0F PdLYURETHANE FILM/SPLIT LEATHER LAMINATE Robert G. Sutton, Philadelphia, Pa., assiguor to Norwood Industries, Inc., Malvern, Pa.

Application .Mar. ;9, 19-70,]Ser.'No. 17,572, new Patent --No. 3,713,938, which is acoutinuation-in-part of applications Ser. .No. 659,101,- Aug. 8, 1967, and Ser. No. 737,116,'Jui1e 14,1968, Divided and this application 0ct;20,' 1971, Ser. No. 191,039 i ,IntJ'CL'BSZb 3/10 U.S. Cl.'161-64 1 3 Claims ABSTRACT DISCLOSURE Production.of laminated articles by casting and drying a; layer. of atully-reactd polyurethane material on a release treated carrier in a'manner to form a moisturevapor-permeable: and moisturedmperme'able film, one or more hides of split leather :being bonded to the supported film through a: moisture vapor-permeable tie-coat of a compatible adhesive, "and the carrier then being removed. The resultant split leather/ polyurethane film product hastheappearance and other properties of top-grain leather. 7 1

This"application is a division of application Ser. No. 17,572, fi1ed Mar; 9, 1970 now Pat. No. 3,713,938, which m ni-r1 is a continuation-impart of application Ser. 1Nos."659,lQ1l and' 7 3 7,116, filed Aug. 8, 1967 and June 14,1968, respectively both now abandoned.

This invention relates to the production of laminated articles'and relates more particularly to the production of "laminatesfrorn a pre-cas't, 'fully reacted polyurethane film bonded to split leather through. a discontinuous tiecoat'of a compatibleadhesive material.

The long-e'stablished art of tanning leather is well documented. Top-graindeathen'is a, veneer of the hide which, afterremoval, leavesa great. deal of leather known as split leatherlff Thus, the termfsplit leather as used herein and inthe appended" claims, is intended to define the *material r'emaining'in' a" leather hide after removal of the 'top-grain veneei as well as reconstituted leathers made from such materials 'by well-known techniques, and is intended to exclude such materials as the top-grain veen'er' itself ands'ynthetic poroifia'ric products, such as Corfam. The ter'mjhide" is intended to apply to the remaining leather portion from an entire animal or any portion thereof. i

The instantinventiveconcepts aresapplicable to split leathers from the skins of various animals, including, forsexample, cattle, goats; calfs, sheep and horses, regardless ofth'emethod of'tannin'g, whether the same be chrome-tanned; aircoiiium tanned, jveg'etable-tanned or tanned by" synthetic tanning agent's? V s Sincef tanningt'echniques "and procedures for the. pro: duction-"of reconstituted 'leather are lwell known in the art,i=and'since these' concepts se ner form a part of the v instant. invention, :furthe'r details regarding same arenot necessary I Splitleathenhas not found a sizablemarket; "other" than a buffed, dyed,,reverse," or suede-leather products.

Due-,to the porosityof-split leather, it'scannot be finished leather is, for certain purposes, a superior part of the hide, the polyurethane film/split leather products of this invention have softer hand, better drape, significantly improved abrasion resistance and flex-fold characteristics than top-grain leather. The products of this invention have all of the advantages of leather, since they are formed primarily of natural leather as contrasted with such synthetic poromeric materials as Corfam which, while porous, do not satisfactorily absorb moisture.

It is important in leather products used, for example, in shoe uppers, that the interior thereof absorb moisture from the foot while moisture is desirably precluded from passing from the exterior to the interior. Yet, while passage of moisture is undesirable, passage of moisturevapor, that is moisture-vapor permeability or breathability, of the shoe upper is recognized to be a necessary characteristic of such materials. Solution or liquid coating of porous material such as split leather, while precluding moisture passage, also precludes passage of moisture vapor, rendering coated products moisture vapor-impermeable.

It is an important object of the instant invention to provide for the production of split leather laminates which, when used as shoe uppers, provide an interior moisture-absorbing material, that is, the split leather itself, with a moisture-proof exterior, while the entire product is moisture-vapor permeable or breathable.

Another important and basic object of this invention is the provision of a simple and inexpensive procedure for the upgrading of split leather to a product having all of the advantageous characteristics of top-grain leather.

Yet another object of this invention is the provision of techniques for forming laminated products in a continuous manner even though the split leather hides being processed are non-uniform in size and shape and, are therefore diflicult to handle in a continuously-operating production line.

Other and further objects hereof will be obvious from the following detailed description which makes reference to the attached drawing wherein:

FIG. 1 is a schematic illustration of the first step of forming products according to this invention;

FIG. 2 is a schematic illustration of further steps according to the process of this invention; and

FIG. 3 is an enlarged fragmentary perspective view of a portion of a product according to the instant inventive concepts prior to removal of the release papers therefrom.

Like reference characters refer to like parts throughout the severalviews of the drawing.

It has been found that the foregoing objects can be satisfied by bonding a precast, fully reacted moisture vapor-permeable and moisture-impermeable polyurethane 5 film in a manner so as to render the same moisturein the s ame manneras-top-grainl leather, si'rrce' the' s'olu tion coatings convenfionally used with top-grain leather willlpenetrate, split leather, resulting in a .boa'rdyproduct'-- with nqactuai topg-finislr. l t has nlot been found that urethane iilms can .be adhesivelylgouded to; split leather,

resultingirr a finish which B actually far ,superior toprecast,- fully reacted polya' conventionally. finished, top-grain; leather. Since split vapor permeable. This is preferably accomplished by casting a-fully reacted polyurethane composition on a release paper in a limited thickness and drying the film to remove solvent therefrom, r'esulting'in a film having plishedaby'those skilled in-the art.

The release paper acts as a'carr'ier for theufilm were is provided with aitie coat'of a compatible adhesive into whichware: laid :the. split leather hides,permitting *c'ontinuousw manufacture of therlaminated products; Additionally, the release papercan also 'beused to provide the outside surface of the film with a'desi'red decorative design and :degree of gloss. r

-'It is also-important, in order to insure breathability in the final product, that the adhesive layer be thin enough that the rough surface or nap of the split leather penetrates the same during lamination to render the tie-coat discontinuous and permit moisture vapor passage therethrough in the resultant laminates.

In practicing the invention, a layer of a fully reacted polyurethane elastomer solution is first applied to release casting papers by standard techniques of knife-over-roll or reverse-roll coating equipment. Then the wet layer is carried through an oven to dry by solvent evaporation to a continuous film on the release paper and the dried film and the paper with which it is in intimate contact may be wound on a core for subsequent use in the laminating process. The supported film, on the release paper, is then bonded to the split leather substrate through a discontinuous tie-coat of a compatible adhesive material which may preferably be of the same composition as the film. A layer of the adhesive is applied to the dried plastic film while it is still on the release paper, using knife-overroll or reverse-roll coating equipment or the like, to pro- Wide a controlled thickness of wet bonding agent on the film. At this point, the split leather hides are laid onto the wet tie-coat. The entire assembly is nipped to a controlled degree to bond the split leather hides to the film, using the release paper as a carrier for one or more of the split leather hides.

Depending upon the adhesive material used, var-ions techniques are required to dry the same. The nipping pressure is such as to render the tie-coat discontinuous by partly pressing the surface of the split leather therethrough, whereby the vapor-permeability of the product is insured. Finally, the release paper is removed to produce the finished leather product.

One known process for finishing leather is to solutioncoat the tanned hide on a topgra'in surface with various lacquers and/or polymer solutions. Only top-grain leather can be finished using this process due to the tightness of the grain which holds the solution on the surface for subsequent drying and recoating. Curtain coating of patent finish on top-grain leather requires several applications of solutions with drying required between applications. This long-established process is time-consuming and costly. In addition, it can only be utilized on whole or top-grain leather. Split leather cannot be finished using solutioneoating techniques because split leather is very porous and would absorb the solutions, rendering the same vaporimpermeable. As a result, there is little use made of split leather in finished products. Suede leather products have been the only significant use made of split leather to date. However, the instant invention of laminating a pre-cast, fully reacted polyurethane ifihn to split leather results in a finished product which can be utilized in any application where finished top-grain leather products are presently being utilized.

Referring now to the drawing, and more particularly to FIG. '1, a roll of conventional release paper is shown at as having a textured surface 12 which provides a similar s'uface on the polyurethane film cast thereon. A fully reacted polyurethane composition 14 is cast on the release paper 10 with a knife 16 over roll 17- or the like metering the thickness of the layer 18 fomed thereon. The

cast layer 10 supported by the release paper 10 is then passed through an oven or the like 20 to dry the film by roled on a coreas shown at 24.

The roll ,jof supported polyurethane 24 may then be ssess shown in'FIG. 2 for production of the: final product. A quantity of .a compatible adhes'ive material 26 is metered .asby a knife 28 over roll 29 0i" the like. to form a layer-'30 thereof on the polyurethane film s urface. one or more split leather hides 32 are laid on the adhesive layer 30 and pressed into the adhesive layer as a by nip rolls 34, the pressure being sutficient to insure that a the rough surface or nap of the split leather hides 32 are pressed into the adhesive 30 to render the same discontinuous, whereby the moisture vapor-permeability of the final product is insured. The thus-forrned laminate may then be passed through an oven or: the like 36 to dry the adhesive material 20.

I Referring now to sjana enlargedt'fragmentary" view of the resultant product is designated generally by the reference nume'rall40 and comprises the split leather 32 as a substrate intimately bonded vto the pre-cast,;fully reacted, polyurethane film 22-.byi'the adhesive material, the roughened surface of the split leather 32, schematically illustrated at 42, being pressed into and through .theadhesive layer so as to render the same discontinuousrTlie release paper 10 may then be removed to form the final product which is moisture-permeable onthe split leather surface, moisture-impermeable on the polyurethane film discontinuous tie-coat of adhesive material.

As indicated, the release paper 10 may be embossed on its contact surface to provide a desired pattern on the contacted face of the polyurethane film. Additionally, the release paper may be of various degrees of gloss depending on the desired gloss on the surface of the polyurethane film in the final product.

While one form of coating equipment hasbeen-illustratively shown in .the drawings, it will be understood that other conventional types of equipmenh'such as re verse-roll coaters may similarly be used. Any device which will supply a controlled thickness of polyurethane material and of adhesive material will be suitable.

Although free films of fully reacted polyurethane may be laminated tosplit leather according to this invention, supported films can similarly-be used. Supported films may comprise a film of polyurethane material bonded to, for example,paper, nonwoven fabrics or a textile material, through a discontinuous layer of tie coat, a further discontinuous layer of'tie coat then "bonding the supported film to the split leather substrate. Thus, the

use of the term pre-cast, fully reacted," polyurethane f film as used herein and in the appended claims is intended to cover such films, whether theybe" free orj supported. The preferred technique of this invention'is "to precast the fully reacted polyurethane material onto the release paper and dry the film by'oven heating or thelik e result-- ing in a continuous, moisture vapor-permeablefilm of from 0.5-5.0 dry mil thickness, preferably 1.5-4.0 mil, and most preferably 1.5-3 .0 dry mil. Afilm of this thickness can be readily formed having satisfactory moisture vapor-permeability properties by' evaporation of the so1- vent during the drying procedure. It is preferred to use a pigmented polyurethane material in order ,to produce a surface layer on the final product of a desired color...

After the film has been dried in intimate contactwith t the release paper, the adhesive material mayfbe applied thereto as shown in FIG 2. It is preferred to ,use an adhes'iv'e material identical with the material used in m formation of thelpre cast itself, although other compatible adhesive materials may be used as explained in more detail hereinafter. The thickness of the tie-coat will depend on the material used, its-percent-solids; the solvents used, etc. A thickness of from 0.5-3.0 dry mils; preferably 0.5-4.5 dry milshasbeen foundsuitableto...

insure that the roughened of the split leather substrate will penetrate the same during the lamination procedure. Again, depending upon the nature of the tie coat, particularly the percent of solids, an initial layer of 2-8 wet mil may be applied whichwill be reduced in thickness on drying.

After laying the split leather hides onto the wet tiecoat, the entire assembly is then nipped under pressure as shown inFIG. 2 and the tie coat dried either in an oven, or at ambient temperatures, depending upon the, nature of the adhesive material. The nipping pressure is not critical so long as sufiicient pressure is applied to penetrate the wet tie-coat by the nap of the split leather. Once the .tie-coat is dried, the resultant laminate may be cut to eliminate the web of release paper between the hides and the release paper may then be stripped from the laminates resulting in a surface polyurethane film, finished in the desired pattern, color and gloss. Alternatively, the release paper may be removed prior to cutting the laminate into the final desired shape.

It is also possible, if desired, to print or post-emboss the resultant laminates to produce a further design depending upon the aesthetics of the final products. Release papers can also be printed in a known manner with a pattern or design which becomes an integral part of the polyurethane film surface when the release paper is removed from the film. It is also possible to print the polyurethane film on the laminating side with various designs and colors while the film is on the release paper.

The wet tie-coat can be pigmented to colors different from the polyurethane film resulting in a multitude of patterns, designs and colors. This technique would produce a pattern which is protected by a layer of polyurethane film above the color design.

Thermosetting polyurethane resins are the preferred materials used in the process of the instant invention, although thermoplastic resins aresatisfactory for some applications. The thermosetting materials lend themselves to shoe fabrication where high heatis used to smooth the leather on the last. Polyurethane films have far superior abrasion resistance to other finishes and can be made breathable due to the minimum thickness required for the final product. The. process of this invention also results in a bond of the polyurethane film to split leather which is several times as great as conventional finishes used.

As pointed out previously, the use of a pre-cast, fully reacted polyurethane film is critical to the production of a laminate with split leather. Since split leather is porous, it cannot be finished using conventional solution coating techniques. I

Although it is believed that the instant inventive concepts can be readily understood from the foregoing, the following specific Examples are set forth to further illustrate the same:

EXAMPLE 1 A layer of a thermosetting, fully reacted, polyurethane resin is cast onto release paper using a knife-over-roll coater and passed through an oven at about 100 C. for about 14 minutes to dry the same and form a film of about 3 dry mil thickness. The polyurethane resin is a polyureapolyurethane in dimethyl formamide. The resin is made by conventional reactions of diisocyanates with glycols which produces an isocyanate terminated prepolymer. The prepolymer is chain extended using aliphatic and/oratomatic diamines and terminated to form a fully reacted resin by using alcohol or other conventional means. The glycols may be either a polyester or a polyether depending on the desired properties of the end product.

The dried polyurethane film is in intimate and tenacious contact with the release paper. A wet laminating compound, preferably of the same composition as used for the polymethane film, is doctored onto the dried film using the same type of coating equipment, to form a layer of about 2-8 wet mil thickness, depending on the roughness of the split leather surface.

The split leather hides are laid onto the wet tie-coat and the entire assembly is passed through a nip at a fixed pressure. The laminate is passed into an oven at about C. for about 2 minutes to dry the tie-coat to a thickness of about 1 mil and the release paper is stripped from the film. e I

Excellent interfacial bonding between the polyurethane film and the splitleather results from the aforementioned technique. The laminate produced can be utilized in any application where conventionally finished top-grain leather has been used heretofore.

The resulting product when tested in accordance with the applicable ASTM test method at 100 F. and 92% RH. has the following water vapor transmission rate in grams/cmP/24 hours:

Finished side as face 438-428 Unfinished side as face 473-626 EXAMPLE 2 A 3 mil polyurethane film is cast on embossed release paper from a solvent-based system and dried at about 100 C. for about 4 minutes.

On this dry polyurethane film is cast a 2.0 mil water emulsion adhesive. The split leather hides are then laid on the wet adhesive and the assembly placed in an oven at about 100 C. for about two minutes to dry the adhesive. The release paper is then stripped from the polyurethane film.

Again, excellent interfacial bonding between the polyurethane film and the split leather results and the laminates resulting therefrom can be used to produce finished leather products where only conventional top-grain leather has been used heretofore.

Drying of the polyurethane film and the adhesive material can be accomplished with ordinary heated ovens or by the use of dielectric heating.

While thermosetting polyurethane films are desired, thermoplastic materials may also be used. Similarly, although it is preferred to utilize a release paper in the manufacture of laminates according to this invention, other conventional casting techniques may be readily substituted therefor. For example, the fully reacted polyurethane material may be cast on a highly polished, continuously moving belt, the surface of which has been treated with a conventional release agent. Moreover, the polyurethane film can be cast on non-embossed, embossed, or patent-finish release paper to obtain the desired finish on the film itself. Post-embossing the laminated product can also be accomplished by conventional embossing techniques. Various designs can be produced in situ on the polyurethane film by printing the release paper with the desired pattern prior to solution casting the film. When the dried film is stripped from the printed paper, the design is transferred to the film and is actually an integral part of the film itself. As indicated, it is also possible to print the polyurethane film with any desired pattern. However, the former technique results in a durable print without the use of top coating for protection against abrasion and moisture resistance.

With regard to the specific materials utilized for the formation of the polyurethane film/ split leather products of this invention, the film is preferably pre-cast from a solvent-based urethane elastomer in thicknesses as indichlorop I nyle is teyanatwoyclohexyleneia 1,4 diis'ocyanate; 4,. diphenyl mare. :COHW QOHQL Y-allsfidriiiiQ- lifliwbsrWithsihf? 01 28-11137; iso- T cyanates to produce the polyurethane :resin'jse: Fon example,

cyanate, 3,3 dimethyl 4,4 diphenylene-diisodyanate,

+=,-.-4,4'1 'ph iyleneadiisoeyanate; tricommerlciallygavailable @arhowaxgil*polyalltylenea glycols {having an averageemolecular weight'of from'aboutfifltito about 750 may be used. Other common materials'inc-lude butylene glycol-2,3, 'butylene glycol-1,3, Z-methylene pentanediol-2,4', styrene glycol decamethylene glycol, and

- the like. Broadly, various polyesters and/or polyester 1 amides may be utilized, including those obtained by condensing polybasic (preferably dibasic carboxylic) organic acids, such as adipic, sebacic, phthalic, isophthalic, tetraphthalic, oxalic, malonic, succinic, maleic, cyclohexylene 1,2 dicarboxylic, cyclohexylene 1,4 dicarboxylic, polyacrylic, naphthalene 1,2 dicarboxylic, fumaric,

itaconic, glutaric, pimelic, suberic, azaleic, and the like, .with polyalcohols, such as ethylene glycol, diethylene glycol, glycerol, sorbitol, triethanolamine, di-(fl-hydroxyf ethyl)ether, and'the like, and/r amine alcohols such as ethanolamine, 3 aminopropanol, 4 aminopropanoljS- "aminopentanol-l, fi-aminohexanol, aminodecanol, 6- amino 5 methylhexanol 1, p-hydroxy-methylbenzylfused heerin and in the appended claims with reference to the material from which the polyurethane film-iscast is to 'be understood to indicate that the polyurethane has no "reactivei'socyanate groups, the reaction being terminated in a conventional manner prior to casting to preclude further cross-linking.

The deposition of the polyurethane is generally preferably accomplished from a solution or dispersion of the same and a suitable solvent, such as inter alia, methylethylketone, methylenechloride, xylene, toluene, and lower 'alkylene alcohols, dimethylsulfoxide, dimethylformamide and methylpyrrolidone.

The aforementioned materials are not intended to be all-inclusive, but do provide a comprehensive list of conventional reactants utilized in the manufacture of polyurethanes suitable for this invention. The specific polynot; adhesive epen suponrthe nd'use of'fth polyurethane :afilm/split leatherilaminate;-zsolvent efiect on gthe' ipoly- .-..zurethaner:i film', e.:euretimer-of their adhs'rye, flamm' bility hazards, ease of application, and cost.

With the above" eonsidehations rinsniind; ha been .ufoundethatcllfilm-forniing -;--iivater emulsion: adhesives are ,epreferred, althougk-solvent-based uretlfanes'ha 'e ztproven equally/= fsuccessfulaissince, many-fsolvents may swell ithe polyurethane film, the-water emlsionsxelimina meanszlisible'zd-rawback.-Thexwaterzemulsion sco'sity'e can be icon- 'trolled forwea'se of-s application 'ithdre .no health-pn :fijre 'hazardv'duefto solvents',-andr apid drying rteasilyeiaccomplishedJDr'ying is usually accomplished-"in 2z'ltos3: minutes at 110 C. Longer drying'=-t'imes' or higher'. temperatures may have detrimentala'efiects on'th'esplit leather. The film thickness of the dried adhesivelayeris.completely dependent on the quality ot the split-leather and on the'end use of the laminate. The mil thicknessiis 'usuailly in'the rangeof13mils..-

.5 Again, the aforementioned materials are' notcintended to be all-inclusive, but merelyrtofprovide a"comprehensive list of commercially available, conventional ,adhesives which may be utilized to bond the polyurethane filrrl to the split leather according to thisinventions'lt is 'only ,portant to select an adhesive Which'iscompatibl'e witlfthe polyurethane film andthe split 'leathen'a -selectionwhich is well' within the skill-of" the art. Preferably, as indicated, the adhesive may be'i-zof the same composition as the material used in formation of thepolyurethanedilm. Since many variations of the --for e'going-i.conceptsmay be contemplated, .it is il-to be understood that all matters herein are to be interpretedfmer el-y tts illustiativ andribt ina limiting sense. 3

What is claimed is: I 1 I I 1. A laminated. article'cornprising.a substrateof'split leather having a rough napiand-a pre cast, fully reacted polyurethane film intimately b'ondedto one surfaceof said substrate by a tie-coat ofla' compat'ible adhesive material, the nap of said split 'leathe'rpenetrating 'said'tiewoatfof adhesive material to render the same discontinuous and moisture vapor-permeable, said'ipolyurethane film-having minute pin holes to. render the "same moisture'vaporpermeable while still maintaining-the moisture-impermea'biiity of said film, whereby said laminated article-has the appearance oftop-grain leather and :is moisture-permeable on the split leather side, 'rnoisture-impermeableon the polyurethane film'side and moisture vapor permeable throughout. s .1 *2

2. The laminated article of claim-1 wherein said ad- -hesive material is polyurethanef i 1 l 3. The laminated-article ofclaim 'Lwhereihshid-iaoljrurethane film has a thickness of 0.5-5 dry mils an'd said tie-coat has a thicknessof Q.53 d ry mils; i i

urethane chosen is not critical, nor is the processing thereef r cs ciifi p of, so long as sufficiently thin films are cast in order to UNITED STATES P S- form a water vapor-permeable and preferably water- 3 298 856 q impermeable film. Using the thicknessesv discussed-above,

such properties can readilybe provided, H I odfitfial t Ma adhesive mat als bond :5'575894" "4/197'1' 20rn er a1 l D i *2 polyurethane ,filrn to the split. leather, Water emulsions,

. A 3,050,432 8/ 1962 Wembrenner et al. l61D1g. 2 solvent solutrons orsohds of natural-and synthetic resins, r H l i 3,418,188 12/1968 Hogg 156246 suchas naturaland synthet c rubbers, epox es such as 565 981 2/1971,

Armstrong Epoxy. 1 1148, asphalts,:- oleoresins such, as 65 Armstrong F l450,- polyamides, hot melts, neoprenes, polyesters, polybutanes, polyarylethers, polysulfones, poly- ,vinylbutynes, nitriles, acrylics, particularly high tempera- .ture cur ing acrylic emulsions, dextrines, acetoxylated polyethylene, phenolics, copolymer emulsions "such as 'Airco Chemical 400, polyurethane polymers -:such as .Bostik 7070, or any polymer-of the'above. The choice 

